1. Field of the Invention
The present invention relates to a semiconductor device tester for obtaining electric characteristics of semiconductor device called BGA (Ball Grid Array) having outer input/output terminals arrayed in lattice on base, especially a semiconductor device tester with a print substrate to print wiring for tester circuit.
2. Description of Related Art
The conventional semiconductor device tester comprises a semiconductor socket for electrically connecting with outer input/output terminals (solder balls) of a semiconductor device to be tested, and a print substrate attaching the semiconductor substrate (c.f. U.S. Pat. No. 5,993,269 Ito).
According to the conventional art mentioned above, as shown in a plan view of FIG. 2(a) and a sectional view of FIG. 2(b), the conventional semiconductor device tester 10 comprises a semiconductor socket 20 and a print substrate 30. The semiconductor socket 20 comprises a stage 21 to decide position of semiconductor device, a probe 22 to obtain electric contact with outer input/output terminal of semiconductor device, a socket base 23 to hold the probe 22, a front lid 24 to keep the probe 22 held in the socket base 23, a spring 25 to separate the stage 21 from the socket base 23, a guide pin 26 to guide the stage 21 in vertical direction over the socket base 23, and a fixing bolt 27 to keep the guide pin 26 held in the socket base 23.
The print substrate 30 is electrically connected, via the probe 22, with the outer input/output terminal of a semiconductor device positioned by the semiconductor socket 20. And, the semiconductor socket 20 is fixed to the print substrate 30 with a socket guide pin 31 and a composing bolt 32. Here, the socket guide pin 31 is to guide the socket base 23 in vertical direction over the print substrate 30.
The print substrate 30 is formed at a thickness of about 3 mm. And, on its front surface, there is a contact terminal for contacting with the probe 22. Further, on its back surface, there is wiring which is electrically contacted with the contact terminal for contacting with the probe 22. A circuit of a tester is formed with wiring on the print substrate 30. And, a measuring apparatus is connected with wiring (of the circuit of the tester). Thereby, electric characteristics of semiconductor device is measured with the measuring apparatus. The probe 22 comprises, as shown in FIG. 3, a ball plunger 33 to contact with solder ball, a substrate plunger 34 to contact with wiring of the print substrate 30, a spring 35 to be put between the ball plunger 33 and the substrate plunger 34, and a case 36 to hold the spring 35, the ball plunger 33 and the substrate plunger 34. The case 36 has a length of about 6 mm and a radius of about 0.5 mm.
The ball plunger 33 comprises an electrically conductive pole having a contact portion 37 or a grip portion 38 at each end of the pole. The contact portion 37 is a portion to obtain good contact with the solder ball. The grip portion 38 is a portion to hold an end of the ball plunger 33 in the case 36. Thereby, the grip portion 38 is movable only in the case 36 in vertical direction with a prescribed stroke, and the ball plunger 33 moves with the grip portion 38 outside of the case 36 in same vertical direction with same prescribed stroke. A pinched portion 39 is formed in the vicinity of top end portion of the case 36. And, the grip portion 38 stops at the pinched portion 39, because inner radius of the pinched portion 39 is smaller than outer radius of the grip portion 38. Thereby, the ball plunger 33 is held in the case 36.
The substrate plunger 34 comprises an electrically conductive pin 40 and a grip portion 41. And, the electrically conductive pin 40 is protruded from a hole formed in base of the case 36. The grip portion 41 stops at the base of the case 36, because inner radius of the hole of the base is smaller than outer radius of the grip portion 41. Thereby, the substrate plunger 34 is held in the case 36.
Moreover, in the case 36 mentioned above, there are electrically conductive balls not shown in the drawings, between the grip portion 38 and the spring 35, and between the spring 35 and the base of the case 36. And, lower end of the grip portion 38 is slanted (c.f. Ito). Then, the grip portion 38 and the ball are pressed to inner wall of the case 36 in opposite direction, when the spring 35 works. Thereby, conductivity of electricity between the grip potion 38 and the inner wall, and between the ball and the inner wall, further between the grip portion and the ball, is secured.
Further, as other prior art, there is a probe without case like case 36 shown in FIG. 3. This kind of probe is put in a hole formed in a socket base like the socket base 23 shown in FIG. 2(b). And, a spring 35 between a grip portion 38 and a grip portion 41 like those shown in FIG. 3, works in the hole formed in a socket base 23. Then, upper portion of this kind of probe contacts with an outer input/output terminal of a semiconductor device. And, lower portion of this kind of probe contacts with a print substrate. Further, a grip portion 38 and a grip portion 41 like those shown in FIG. 3, contact with each other, when the spring 35 shrinks.
Meanwhile, whichever probe mentioned above is adopted, base of the probe makes contact with a contact terminal of a print substrate, and the contact terminal electrically makes contact with wiring formed beneath back face of the print substrate. Therefore, the semiconductor device electrically makes contact, via the probe, with wiring of a tester circuit formed on the print substrate.
The conventional tester device shown in FIG. 2 operates as follows. A semiconductor device to be tested, is put on the stage 21. There, the semiconductor device is positioned. Thereafter, the outer input/output terminal of the semiconductor device makes contact with the probe 22 (ball plunger), when the stage 21 comes closer to the socket base 23. Further, spring of probe 22 put in the socket base 23 shrinks, when the stage 21 comes even closer to the socket base 23. Then, good conductivity of electricity is secured between the outer input/output terminal of the semiconductor device and the probe 22. As mentioned before, the probe 22 is electrially connected with the tester circuit on the print substrate 30. Therefore, the semiconductor device is electrially connected, via the probe 22, with the tester circuit on the print substrate. Then, in this situation, electrical characteristics of semiconductor device is measured.
Meanwhile, a semiconductor device in these days, operates very fast with fast clock. Therefore, fast signal is inputted or outputted through input/output terminal of semiconductor device, which operates according to such a fast signal. This fast signal transmits between the semiconductor device and the wiring formed on the print substrate, via the probe 22.
Meanwhile, this kind of fast signal delays, owing to distance from the outer input/output terminal to the wiring (for the tester circuit); that is, distance of about 9 mm; consisted of about 6 mm of length of the probe 22, and about 3 mm of thickness of the print substrate. Therefore, by delay of transmission of fast signal, the conventional semiconductor tester device could not measure proper characteristics of a semiconductor device. And, this is a problem.
Therefore, the present invention aimed at providing a semiconductor tester device to be able to measure proper characteristics of a semiconductor device.